This invention relates to an ignition control circuit for an internal combustion engine for automotive and like applications. The invention also relates to an engine system comprising an internal combustion engine with at least two ignition coils and having such an ignition control circuit. The ignition control circuit in accordance with the invention may comprise a separate power semiconductor switch for each ignition coil, and a further circuit device common to all the power semiconductor switches.
Traditional ignition control circuits have a single ignition coil controlled by a contact breaker and ballast circuit arrangement and coupled to a 1 to 4 or 1 to 6 (depending on whether the internal combustion engine has four or six cylinders) high tension distributor to enable the combustion cycles of the individual cylinders to be controlled in the desired sequence to enable correct operation of the internal combustion engine. Such an arrangement requires a number of mechanically complex moving components such as the contact breaker and distributor and it can be difficult to ensure that the timing sequence of the firing of the cylinders remains accurate, especially over long periods.
In recent years electronic ignition systems have been introduced into automobiles. In this case, complex mechanical parts are replaced with solid state components that allow microprocessor or computer control so enabling more precise control of the operation of the internal combustion engine. In order to avoid the need for a distributor, it has recently been proposed to provide a number of ignition coils so that, at most, two cylinders share a common ignition coil and to provide a separate solid state switching and current limiting circuit for each ignition coil to replace the contact breaker and ballast of a conventional internal combustion engine.
Each such switching and current limiting circuit typically requires a power semiconductor switch and a complex control circuit. Generally these have to be provided as separate components and cannot be integrated together without the use of very complex and thus costly buried layer semiconductor isolation techniques, because inherent parasitic bipolar structures within the integrated circuit may cause detrimental and even irreversible breakdown at the high voltages experienced in internal combustion engine ignition control systems. Such problems are especially likely to arise where the power semiconductor devices used are Insulated Gate Bipolar Transistors (IGBTs). As is well known to those skilled in the art of power semiconductor switches, IGBTs basically have a power MOSFET structure but are provided with an anode region to inject opposite conductivity type carriers (holes in the case of an n-channel MOS structure) into the drain drift region of the MOS structure to reduce the on-resistance of the power semiconductor switch. The use of IGBTs is advantageous because an IGBT can achieve a lower on-state voltage drop for a given voltage rated device than the corresponding power MOSFET (IGFET).